Mechanisms of perineal tear during childbirth

International audienceThe perineum is a multi-layered structure made of soft tissues whose mechanical properties ensure the integrity of the pelvic floor,<br&gtparticularly in women. During childbirth, the perineum undergoes very large deformations which often lead to tears going from the skin and vagina to the anus. In the long term, these tears cause urinary and anal incontinence as well as pelvic organs prolapse

In-vitro biomechanical properties of porcine perineal tissues to better understand human perineal tears during delivery

International audienceIntroduction:Data concerning the mechanical properties of the perineum during delivery are very limited. In-vivo experimentations raise ethical issues. The aim of the study was to describe some of the biomechanical properties of each perineal tissue layer collected from sows in order to better understand perineal tears during childbirth.Material and methods:Samples of each perineal tissue layer were obtained from the skin, the vagina, the external anal sphincter (EAS), the internal anal sphincter (IAS), and anal mucosa of fresh dead sows. They were tested in quasi-static uniaxial tension using the testing machine Mach-1®. The tests were performed at a displacement velocity of 0.1 mm.s-1. Stress-strain curves of each perineal tissue layer before the first damage for each sow were obtained and modeled by hyperelastic Yeoh model described by three coefficients: C1, C2, and C3. Pearson correlation coefficient was calculated to measure the correlation between C1-coefficient and the duration between the first microfailure and the complete rupture for each perineal tissue layer. Pearson correlation was computed between C1-coefficient and the number of micro-failures before complete rupture for each tissue.Results:Ten samples of each perineal tissue layer were analyzed. Mean values of C1-coefficient and corresponding standard deviations were 46 ± 15 kPa, 165 ± 60 kPa, 27 ± 10 kPa, 19 ± 13 kPa, 145 ± 28 kPa for the perineal skin, the vagina, the EAS, the IAS, and the anal mucosa, respectively. According to this same sample order, the first microfailure in the population of 10 sows appeared at an average of 54%, 27%, 70%, 131%, and 22% of strain. A correlation was found between C1 hyperelastic-coefficient and the duration between the first microfailure and the complete rupture (r=0.7, p=0.02) or the number of micro-failures before complete rupture only for the vagina (r=0.7, p=0.02).Conclusions:In this population of fresh dead sow’s perineum, the vagina and the anal mucosa were the stiffest tissue. The IAS and EAS were the more extensible and the less stiff. A significantly positive correlation was found between C1-coefficient and the duration between the first microfailure and the complete rupture of the vagina, and the duration between the first microfailure and the complete rupture of the vagina

Modeling clinical situations at risk of perineal tear during delivery

International audienceModeling clinical situations at risk of perineal tear during deliver

Vers une modélisation multi-échelles du comportement mécanique du périnée

National audienceLes dysfonctions et anomalies du tissu pelvien sont responsables de nombreuses consultations et interventions chirurgicales chez la femme au cours de sa vie et de la grossesse ; elles sont principalement attribuées à la dégradation ou à l'évolution de ses propriétés biomécaniques. Pour le clinicien, il est essentiel de connaître le comportement mécanique de ce tissu afin d'anticiper sa dégradation. L'objectif de ce travail est de proposer une modélisation de ce tissu en le considérant de façon simplifiée comme un matériau multicouche. La modélisation s'appuie sur les résultats de tests de traction large instrumentés avant rupture couplés à des essais de relaxation réalisés à des paliers de déformations réguliers sur de périnées de cochons à partir desquels sont prélevés des échantillons de peau, de tissus conjonctifs et de muscles de sphincters anaux. Ces différents tissus peuvent être modélisés à travers un comportement hyperviscoélastique avec des paramètres de viscosité déterminés à chaque palier de déformation marquant l'évolution de la microstructure des tissus avec la déformation équivalente. Une méthode de recalage par éléments finis est utilisée pour déterminer les paramètres du modèle pour chacun des tissus testés. Une modélisation simplifiée du comportement hyperviscoélastique du périnée est alors proposée